A press briefing on the Australian future submarine (FSM) program by Jean-Michel Billig, the Australian program director for Naval Group (formerly DCNS), at the PACIFIC 2017 international maritime expo a few weeks ago set some hares running. Among other things, he said that ‘The vessels may end up with conventional propellers as well as air independent propulsion, which helps to increase underwater endurance’.
That was significant because DCNS made a big deal of offering Australia pump-jet propulsion during the competitive evaluation process for the FSM. We were told that ‘The Shortfin Barracuda uses a pump-jet propulsor that combines a rotor and stator within a duct to significantly reduce the level of radiated noise [compared with propellers] and avoids cavitation’. And DCNS Australia’s CEO really played up the significance of the technology:
There’s no better example of [the benefits of a strategic Australia–France relationship] than the offer from France to transfer to Australia sovereign control and use of pump-jet propulsion technology for the Shortfin Barracuda—technology resident only in France, the UK and the USA. Technology born from the French SSBN program a generation ago. The stealth and hydrodynamic performances of pump jet propulsion are of course classified and in Australia known only to DCNS and the Australian Government.
While no hard data has made its way into the public domain, an argument began doing the rounds among submarine tragics that pump jets are too inefficient at low speeds to make sense on a conventional submarine. (See here, for example, and I’ve had a stack of correspondence along those lines.) The recent Insight Economics report (PDF) has a chart (p. 103, redrawn below) that seems to show that pump jets turn electrical power into propulsion less efficiently than propellers at low speeds, though they are superior at higher speeds.
Clcik on this link for a detailed technical discussion on the merits of the propulsion systems: